In Vivo Fitness Cost of the M184V Mutation in Multidrug-Resistant Human Immunodeficiency Virus Type 1 in the Absence of Lamivudine

Abstract

Lamivudine therapy selects for the M184V mutation. Although this mutation reduces the replicative capacity of human immunodeficiency virus in vitro, its impact on viral fitness in vivo has not been well defined. We used quantitative allele-specific PCR to precisely calculate the fitness differences between the mutated M184V virus and one that had reverted to the wild type in a cohort of patients by selectively interrupting reverse transcriptase inhibitor therapy, and we found that the M184V variants were consistently 4 to 8% less fit than the wild type in the absence of drug. After a lag phase of variable duration, wild-type variants emerged due to continued evolution of pol and back mutation rather than through emergence of an archived wild-type variant.Despite recent advances, the management of multidrug-resistant (MDR) human immunodeficiency virus type 1 (HIV-1) remains a major clinical problem. One strategy to avoid immune deterioration while minimizing toxicity in viremic patients infected with MDR HIV-1 is to prevent the emergence of wild-type (WT) HIV-1 by continuing selected drugs in a failing antiretroviral regimen. Studies show that reverse transcriptase (RT) inhibitors (RTIs) continue to exert antiviral activity in the presence of resistance mutations(8, 21). In particular, continuation of lamivudine (3TC) or emtricitabine in the presence of the M184V mutation may provide clinical benefit (3, 4). We previously showed that M184V is lost at a median of 20 weeks following interruption of 3TC together with other RTIs while the use of protease (PR) inhibitors (PIs) was continued in viremic subjects with MDR HIV-1(8). In this study, we performed a detailed analysis of the decay of the M184V-carrying mutants in these individuals.(

Vicriviroc Resistance Decay and Relative Replicative Fitness in HIV-1 Clinical Isolates under Sequential Drug Selection Pressures

“…The relatively rapid decay of HIV-1 VCV resistance in this individual was most consistent with the reemergence of sensitive virus from a preexisting variant rather than the back mutation of multiple V3 loop amino acid substitutions (23,40). Deep sequencing confirmed that the dominant week 48 V3 loop sequence was present as a minor variant in the week 0 plasma sample.…”

“…The sampling of more time points during these weeks would have permitted an exact quantification of the total plateau time, as well as a precise determination of the start of resistance decay. The persistence of resistant viruses in plasma for several weeks after drug discontinuation has been observed in patients infected with NRTI-and enfuvirtide-resistant viruses (31,40). The maintenance of a less fit viral variant in plasma, followed by the rapid extinction of this variant, may reflect the time interval between drug discontinuation and the stochastic activation of a cell or cellular population that harbors the archived wild-type viral variant.…”

“…The quantification of VCV-resistant and -susceptible variants by clonal sequence analysis of V3 from serial plasma samples showed an estimated fitness disadvantage of 10 to 11% for VCV-resistant viruses in the absence of VCV. In comparison, reported fitness disadvantages associated with enfuvirtide, didanosine, or lamivudine resistance range from 4 to 65% (9,29,31,40,54). No decay in VCV resistance mutations was observed in the first 3 weeks after VCV discontinuation.…”

“…Increased fitness in one environment may result in reduced fitness in another, and the removal of a drug selection pressure may lead to equally dramatic population shifts back toward viruses that do not contain resistance mutations (7, 31). The HIV-1 env gene plays a major role in determining viral fitness due to envelopemediated differences in the efficiency of receptor binding and the kinetics of entry (27,34,46,57).Viruses that dominate after drug discontinuation are derived either from previously archived wild-type genomes or, if no such wild-type virus exists (e.g., in the case of transmitted drug resistance), from back mutation and selection (20,23,40). In vitro and in vivo studies have quantified the fitness costs of a range of specific resistance mutations to nucleoside reverse transcriptase inhibitors (NRTI), nonnucleoside reverse transcriptase inhibitors (NNRTI), protease inhibitors (PI), and entry inhibitors (enfuvirtide) (11).…”

“…Viruses that dominate after drug discontinuation are derived either from previously archived wild-type genomes or, if no such wild-type virus exists (e.g., in the case of transmitted drug resistance), from back mutation and selection (20,23,40). In vitro and in vivo studies have quantified the fitness costs of a range of specific resistance mutations to nucleoside reverse transcriptase inhibitors (NRTI), nonnucleoside reverse transcriptase inhibitors (NNRTI), protease inhibitors (PI), and entry inhibitors (enfuvirtide) (11).…”